The tells us how many protons are in the nucleus for any given element

The tells us how many protons are in the nucleus for any given element.

Oxygen is atomic number 8.

Therefore, its nucleus contains 8 protons.

Protons are positively charged. One proton has a charge of ##+1##. In order for the atom to be in a neutral state, we need something to counter the charge of the proton. So we have electrons, which are negatively charged. One electron has a charge of ##-1##.

So the atomic number not only tells us the number of protons in an atom, but also the number of electrons.

Oxygen has 8 protons, and 8 electrons.